Endogenous Dopamine Maintains Synchronous Oscillation of Intracellular Calcium in Primary Cultured-Mouse Midbrain Neurons

We demonstrated synchronous oscillation of intracellular Ca²⁺ in cultured-mouse midbrain neurons. This synchronous oscillation was thought to result from spontaneous and synchronous neural bursts in a synaptic neural network. We also examined the role of endogenous dopamine in neural networks showing synchronous oscillation. Immunocytochemical study revealed a few tyrosine hydroxylase (TH)-positive dopaminergic neurons, and that cultured neurons expressed synaptophysin and synapsin I. Western blot analyses comfirmed synaptophysin, TH, and 2 types of dopamine receptor (DR), D1R and D2R expression. The synchronous oscillation in midbrain neurons was abolished by the application of R(-)-2-amino-5-phosphonopentanoic acid (AP-5) as an N-methyl-D-aspartate receptor (NMDAR) antagonist. This result suggests that the synchronous oscillation in midbrain neurons requires glutamatergic transmissions, as was the case in previously reported cortical neurons. SCH-12679, a D1R antagonist, inhibited synchronous oscillation in midbrain neurons, while raclopride, a D2R antagonist, induced a transient increase of intracellular Ca²⁺ and inhibited synchronous oscillation. We consider that endogenous dopamine maintains synchronous oscillation of intracellular Ca²⁺ through D1R and D2R, and that these DRs regulate intracellular Ca²⁺ in distinctly different ways. Synchronous oscillation of midbrain neurons would be a useful tool for in vitro researches into various neural disorders directly or indirectly caused by dopaminergic neurons.